In recent years, many low calorie or non-calorie foods and beverages have been marketed for the increase of a disease due to life style such as a metabolic syndrome, or consciousness to health. A substitute sweetener such as a sugar alcohol and an artificial sweetener is mainly used in these products. A sugar alcohol has low sweetness compared to sugar, but is not easily digested and absorbed in the living body. In addition, an artificial sweetener represented by aspartame or Acesulfame K is not easily absorbed in the body or has high sweetness, and thus can impart sufficient sweetness with a low amount. As such, a substitute sweetener can realize a low calorie food or beverage without impairing palatability, and thus is useful.
However, the taste quality of a substitute sweetener is not uniform. In order to impart desired sweetness, a substitute sweetener needs to be used in combination with a different sweetener. For example, aspartame is somewhat slow in rising of sweetness, and has aftertaste of sweetness. Meanwhile, Acesulfame K is early in rising of sweetness and has sharp sweetness. Therefore, combinational use of the two sweeteners presents sweetness closer to natural sugar. In addition, Acesulfame K has a problem of residual aftertaste of bitterness, and is used in combination with another sweetener to suppress the bitterness. In addition, glycyrrhizin, which is a natural product-derived sweetener, is a component that is slow in the rising and strong in aftertaste of sweetness, and the sweetness thereof lasts for a certain time.
A substitute sweetener was originally developed for saving cost. However, these days, a substitute sweetener is considered to be one of means to characterize a product and to add high value to the product to meet various low calorie-oriented consumer needs. Namely, in order to obtain characteristic sweetness that is rich in variety, a substitute sweetener having different taste quality from that of an existing sweetener is desired. Particularly, a long-lasting sweetener is expected for a function such as flavor-reinforcing and flavor-masking. A long-lasting sweetener is highly useful in that it can provide a more delicious food and can reasonably control calorie or sugar intake amount.
A screening for sweeteners using a sweet taste receptor-based assay has been developed since a sweet taste receptor was identified. Guided by the activity against the sweet taste receptor, a component imparting or reinforcing sweetness has been identified (Non Patent Literature 1).
Meanwhile, as a substance imparting sweetness, a component having another activity other than the agonist activity is also conceivable. As one example, lactisole is taken (Non Patent Literature 2). Lactisole has an antagonist activity for a sweet taste receptor, namely, has a sweetness inhibitory effect (Non Patent Literature 2). However, when the lactisole is contained in the mouth, and then water is drunk, the sweetness is induced. The action mechanism thereof is considered to be an inverse agonist activity of lactisole (Non Patent Literature 2). According to the literature, a sweet taste receptor, which is a G protein-coupled receptor, is constitutively active. An inverse agonist such as lactisole decreases the activity below its basal level. When water is drunk in the state where the basic activity is suppressed, the ligand and the receptor are dissociated, and the sweetness receptor returns to the basal state of being weakly activated, and as this time, the sweetness is considered to be induced. In addition, when lactisole is previously contained in the mouth, and a sweetener is taken in the state where the basal activity of the sweetness receptor in the oral cavity is lowered, sweetness reinforcing effect is observed (Non Patent Literature 3). As described above, as a method of inducing sweetness, use of an antagonist such as an inverse agonist is also conceivable.
Sodium chloride is abundant in a normal diet. There is no concern of deficiency in a normal life. However, if a lot of sodium is lost, and the sodium concentration in the blood decreases in the case of a large amount of sweat being bled due to sports, vomit or diarrhea, and heatstroke, it becomes necessary to adequately supply minerals including sodium. For example, it is instructed by Ministry of Health, Labour and Welfare to drink fluid frequently, and take suitable salt in order to prevent heatstroke.
However, if the concentration of mineral components increases in a case where the mineral components are blended with a food and a drink, there are problems that saltiness becomes strong, and the palatability falls. Accordingly, means for inhibiting such saltiness is demanded, and, for example, a method of masking saltiness by adding a saccharide such as inulin (Patent Literature 1) and D-psicose (Patent Literature 2) is known.
In recent years, a voltage-independent sodium channel (hereinafter, also called “ENaC”), of which the activity is inhibited by amiloride, was found as one of the receptors for such saltiness in the oral cavity. It is known that amiloride suppresses only about half of saltiness to the total sense in the oral cavity, inhibiting saltiness in the anterior part of the tongue, but not inhibiting saltiness in the posterior part of the tongue (Non Patent Literature 4). From this, it is considered that amiloride non-sensitive receptors for saltiness are present in addition to ENaC as a receptor for saltiness in the oral cavity, and it is suggested that receptors for bitterness and sour taste are involved as the receptors. Specifically, it is considered that ENaC is involved in a low concentration of 100 mM or less of saltiness, and a receptor for bitterness or sour taste is involved in a high concentration of saltiness (Non Patent Literature 5). Accordingly, it is considered that inhibition of ENaC is effective in inhibition of low concentration of saltiness.
In addition, ENaC is expressed in many human epithelial tissues (for example, the kidney, the bladder, the lungs, the respiratory tract, the salivary gland, and the sweat gland) in addition to the taste bud, and is a route for influx of sodium ion (Non Patent Literature 6). For example, in the kidney, minute control of the sodium amount in the body by means of re-absorption of sodium in the cortical collecting duct is known, which has very important role in regulation of, for example, the body fluid amount, the plasma osmotic pressure, and the blood pressure. Furthermore, it is reported that over-expression or hyperactivity of ENaC is relevant to diseases including hypertension and renal function deterioration, such as cystic fibrosis, pulmonary edema, ulcerative colitis and diarrhea, and ENaC inhibitor is useful for preventing or improving such diseases (see Non Patent Literature 6).
Among known alkenyl sulfate esters, cis/trans-3-decenyl sulfate is reported to be a kairomone-like substance inducing morphological change in green algae (Non Patent Literatures 7 and 8), and trans-3-decenyl sulfate to have an anti-bacterial activity (Non Patent Literature 9). However, an alkenyl sulfate ester adjusting sweetness or saltiness and having ENaC inhibiting action is not known at all until now.